1. Field of Endeavor
The present invention relates to filtering and more particularly to a method of concurrently filtering particles and collecting gases.
2. State of Technology
The conventional disposable High Efficiency Particulate Air (HEPA) filter system used today was originated during World War II when the Allies became concerned for the soldiers who were being exposed to dense chemical fog used for camouflage and/or chemical warfare. Research for breathing apparatus to filter the chemical fog began with creating an aerosol of minimal and uniform particle size to use for instrumentation calibration. The resulting material was dioctyl phthalate (DOP), a pure phthalic ester. The DOP testing method is still used today. An improved filter media consisting of finely ground asbestos and large diameter support fibers was introduced during the early 1950's. This filter media demonstrated a filtering efficiency of 99.97% and was replaced just a few years later during the mid-1950's with a material boasting of uniformity and higher efficiency. We know this material today as fiberglass. The fiberglass material also demonstrated a minimum filtering efficiency of 99.97%; this specification for HEPA has remained unchanged and is still used today.
Most air/gas filter units are constructed the same way—a continuous length of filter media is folded back and forth into pleats and corrugated separators are inserted between each fold. The assembly is then sealed into a rigid, open-faced rectangle. The components of a fabricated filter include: (1) extensively pleated filter medium (including a binder), (2) separators that provide air passages and keep adjacent pleats apart, (3) a rigid filter case that encloses and protects the fragile filter medium, (4) sealants used to bond the filter pack (consisting of the assembled pleated medium and separators) to the filter case and to eliminate leak paths between filter pack components, and (5) gaskets attached to the filter case on one or both open faces to provide an airtight seal between the filter and the mounting frame.
The conventional system used today to capture/collect gases is scrubbers or activated charcoal/carbon filters. Activated carbon is used to trap iodine releases from a nuclear reactor. Activated carbon, often impregnated with iodine or sulfur, is also widely used to trap mercury emissions from coal-fired power stations, medical incinerators, and from natural gas at the wellhead. Activated carbon is also used to capture volatile organic compounds (VOCs).